9
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 4 inches
60,000 5 inches
80,000 5 inches
100,000 6 inches
120,000 6 inches
140,000 7 inches
160,000 8 inches
Air Duct must be
at least 1 sq. in.
per 4,000 Btuh of
total input rating.
Ducts must
extend above
attic insulation.
Air Duct must be
at least 1 sq. in.
per 4,000 Btuh of
total input rating.
at each end of attic
Attic
Insulation
12" Max
Furnace
Water
Heater
Vent or
Chimney
Through Vertical Ducts
Space or Vented Attic
Water
Heater
Vent or
Chimney
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Furnace
Ventilation Louvers For
Unheated Crawl Space
-
-
-
-
-
-
-
-
-
Inlet Air
Ventilation Louvers
(each end of attic)
NOTE: Air openings shall
each have a free area of
not less than one square
inch per 4,000 Btuh of the
total input rating of all
equipment in the enclosure.
-
-
-
-
-
-
-
-
-
Alternate
Air Inlet
Outlet
Air
ducts, the openings and ducts must have a minimum free
large as the free area of their respective openings to the
.
wall, the two openings must each have free area of at
.
Through Horizontal Ducts
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 5 inches
60,000 6 inches
80,000 7 inches
100,000 8 inches
120,000 9 inches
140,000 10 inches
160,000 10 inches
Furnace
Water
Heater
Air Ducts must be
at least 1 sq. in.
per 2,000 Btuh of
total input rating.
Vent or
Chimney
Air Duct
Air Duct
TOTAL INPUT
RATING (BTUH)
MINIMUM FREE AREA
(EACH OPENING)
ROUND DUCT
DIAMETER
40,000 4 inches
60,000 5 inches
80,000 5 inches
100,000 6 inches
120,000 6 inches
140,000 7 inches
160,000 8 inches
NOTE: Each opening to outside
must be at least 1 sq. in. per
4,000 Btuh of total input rating.
12" Max.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Furnace
Water
Heater
Vent or
Chimney
12"
Max
See
Note
See
Note
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